Agricultural feed mixers, often termed Total Mixed Ration (TMR) Mixers, have a goal of providing a homogenous mixture of ingredients that constitute a ration to be fed to livestock for maximum production, whether that production be milk or meat.
There are known methods of controlling the transmission of power from the main power source, usually a tractor engine, connected to the mixing element(s) of a livestock feed mixer by means of a power-take-off shaft (PTO). Traditionally this had been done by using a direct drive connection from the tractor engine, through the PTO, to the mixing elements. Variation in the speed of the mixing elements in a direct drive arrangement is achieved by varying the speed of the engine of the tractor. The advent of larger systems and the attendant increase in power demand brought about the use of a multi-speed gearbox (transmission) having at least two speed ranges or ratios, where a first speed produces a lower output speed than a second speed, but requires less power. One known method of selecting or shifting between the first speed and the second speed is by manual actuation of a shift lever. This method forces the operator to stop the PTO, manually shift the lever to change gears, and then engage the PTO again with the transmission in the different gear, to resume mixing at a different speed. This method wastes time for the operator and reduces the efficiency of the mixing process. This solution also relies on the operator to decide to shift the gearbox at an appropriate time, so as to avoid damage to the drive system components (tractor, engine, drivelines, multi-speed gearbox, mixing element gearbox/reducers), by exceeding their designed loading limits. For an operator, some of the primary indications of the magnitude of loading on these components are visual cues of how full the mixing chamber is, the weight inside the mixing chamber if equipped with a scale system, and possibly an audible cue of the strain on the main power source, such as the tractor engine.
A feed mixer equipped with a weight responsive transmission for example is described in U.S. Pat. No. 7,341,372. The transmission described there is an automatically shifting transmission, which includes a control unit that shifts the gearbox based on the total weight in the mixing chamber.
U.S. Pat. No. 5,462,354 (the '354 patent) discloses a livestock feed mixer directed to the use of an automatic transmission to deliver power from the primary mover to the mixing element of a feed mixer. The transmission described, a Central Detroit Diesel-Allison Inc. AT-545, is a conventional truck automatic transmission. It is an object of feed mixer disclosed in the '354 patent to provide a transmission system which will efficiently drive the mixing process as well as protect the drive train components. The solution presented falls short of its goals in both driving the mixing elements in an efficient way and effectively protecting the drive train components. It is desired, in the application of a feed mixer, to complete the task of mixing ingredients as fast as possible to reduce valuable time. The truck transmission described in the '354 patent is shifted in response to changes in the output speed of the transmission. Many times this style of transmission will force itself into a lower gear (i.e., speed range), when in fact the primary mover has sufficient horsepower to drive the unit at a higher speed. Systems such as this have the disadvantage of very long processing time, which for the application of a feed mixer, is considered a loss of efficiency. Additionally, the transmission described does not support safeguards to prevent a condition which would find the transmission in a “sour spot” (opposite of a “sweet spot”) that causes the transmission to repetitively shift back and forth between a lower gear and a higher gear. Due to the nature of various mixing materials, rapid changes in the torque required to do the mixing, and in the resulting output speed of the mixer, may occur. An example is when a large round hay bale is added to the mixer. An ingredient such as that may have a solidly compact core and may produce large spikes in power demand as the bale is caught between the mixing element and the side wall of the mixing chamber. For the transmission described in the '354 patent, the transmission may detect a spike and shift to a lower gear, and when the spike is gone, it may then shift back to a higher gear. This constant shifting back and forth will produce extensive stress and wear on the drive train components, including the transmission itself.